My Possible Project (1990 Suburban)

[wakeup]

I have a 1990 2wd 3/4 ton suburban with the 6.2, th400, and i'm assuming, 14 bolt rear with unknown gears. Picked it up just before this deployment because we needed something cheap that had at least 7 seat belts and could tow. It does all that, plus gets about 20 mpg on the highway, so I'm pretty happy with it.

My wife thinks we should sell it and get something newer. Boo.

I'd like to do a couple of things with it and i'm looking for some ideas and feedback. Some of these things probabably go against rational thought or contradict each other, so bear with me.

For fun, I'd like to lift it. This would include using a method similar to "Bucannan" which means 4" lift spindles off of a 88 to 99. Hopefully this will allow me to clear 35's. Next would be a selectable locker in the rear, and possibly gears while I'm in there. If the spindles don't make enough room for the tires i could do as much body lift as needed (up to 3 inches) to make up the difference. I believe this will work because I currently have 32's on it and you couldn't make them rub if you tried. Any other ideas or objections or thoughts about this lift plan?


Second, I would like to make a little (or a lot) more power. I've thought about a banks turbo, finding a 6.5 turbo donor, swapping in a 6bt or duramax. I really don't have the time or money for a 6bt swap, let alone a duramax. What I'm looking for are things that are more simple or cheaper than any of these options. How do they respond to headers/exaust? Are there adjustments I can make to the fuel pump? Any thing like that. All ideas welcome!

Last, is fuel. I'm hoping that some of the things i do for power might make it possible to get better milage, if not, oh well. I don't know where else to start besides keeping it in good working order with the right tire pressure. Maybe swapping in a 700r4 or overdrive unit? Maybe there's something cheaper that I've over looked, this is my first diesel.


Anyway, Please convince me that this truck is worth keeping by providing some ideas and feed back for what to do with it. Even if it's way off from what I'm thinking now, nothing is set in stone.

Semper Fi,

Wakeup

[wakeup]

Not sure if this worked, but there should be a picture of the burb, so you know what it looks like. There should also be another pic that is one more reason to put bigger tires on it. Not naming names but "she" was still learning to back what she considers to be a long vehicle. (That ditch is at the end of our driveway

[cal30_sniper]

Semper Fi Brother. Nice looking truck.

I have about 0 experience with the diesels in these trucks, but I do have a lot with the transmissions. If it were mine, I would not swap out the TH400 for a TH700. The 700 is a good trans when done right, but it's hard to get there (and often expensive as well). If you're looking for a gas mileage boost, check out gear vendors overdrives. The TH400 is one of the most common applications for a gear vendors, and you can find them pretty regularly on craigslist and ebay. I'm in the process of finding one for my 454/TH400 powered C20 burban right now.

The TH400 is one of the strongest automatics ever built for passenger cars/light trucks. It's right up there in strength with 727 torqueflite, and way ahead of the TH700. With a gear vendors, you're basically adding a .78:1 overdrive to the back of your TH400. In my opinion, that's a better 4th gear to have than the .70:1 overdrive of the TH700. That's a lot of overdrive to be pulling in a big vehicle with really bad aerodynamics at highway speed.

If you're planning on going to 35"ers from the 32"ers that are on there, better look at 4.10:1 gears or better. You should have 3.73:1 gears in there now (possibly shallower due to the diesel). You'll want to increase the gearing to get your cruising RPMs back up to where they should be. Increasing the tire size and adding an overdrive without changing the gears could be result in a 4th gear that you can't really use.

That's just my suggestions, I'm sure others on here will have some great input too.

-cal30sniper

[cal30_sniper]

Also, the TH700 have some pretty bad gearing for a large truck. First gear is really steep, but you have to make a huge leap from 1st to 2nd (almost as much ratio change as 1st to 3rd in some other transmissions). This leads to a really sluggish 2nd gear performance, and some pretty odd ranges where the transmission will and will not downshift.

The TH400 in my C20 has a lot more useable spacing than the TH700 in my R1500. Even in a car as light as my GTA, the huge 1-2 shift gap of the TH700 tends to really bog down the acceleration.

-cal30sniper

[wakeup]

I was worried about that gear jump from first to second in a 700 as well. Sometimes I notice it in the SS, which has 4.10 gears, less weight and twice the usable power of that tired 6.2. I would think that the large jump would be even more pronounced with this diesel because you only have about 2,000 rpm of usable range, vs about 4,000 in a gas v8. I wouldn't be suprised if the burb had 3.55 or even higher (numerically lower) based on how fast i've "cruised" down the interstate. It's hard to tell with out a tach or just opening up the diff though.

[Dieselburb86]

When I had my dad's 86, it was a half ton! The burb was a 6.2 J code, with 3.42 gears and a 700r4. Being that yours is a 3/4 ton, they just might be 3.73s.

[cal30_sniper]

It's easy to tell, at least to get really close. Jack up the rear and put it on jackstands, with the trans in neutral. Make a mark on the driveshaft and one on the bottom of one of the tires. Spin the tire one complete turn, so the mark is back where it started. Count the number of times the driveshaft turns. If it turns slightly less than 3 and a half, then it's a 3.42. If it turns 3 and a quarter, then it's 3.73, so on and so forth.

You can also check the RPO codes if you can find the sticker. It will have the axle ratio listed.

-cal30sniper

[wakeup]

I'll be able to do that when I get home in May. I've used that method before but I didn't even think about it. I may pull the diff cover anyway to change and check the condition fo the fluid. If I was the only one to drive it I would probably put a detroit in the rear while it was open, but my wife wouldn't be happy with the driving manners. And if she takes it to the mountains in the winter, with the possiblility of iced roads, I would rather her have an open diff. I'll put a selectable of some sort in it eventually, I just don't know enough about their reliability to chose what type (electric, air, cable, etc...).

By the way, does anyone reading this know about what the max rpm's these engines will turn is? I took a 600 mile road trip with it to pick up my k10 from florida. On the way to get the truck I was able to maintain about 85 mph without any isssues. My main reason was to see if the cooling system could keep up with the engine under stress at interstate speeds. It maintained about 200 to 210 degrees during those higher speeds. However, I think that was probably right at the top of the rpm range that the engine wanted. Anyway, that speed is what makes me think it has 3.42:1 or so in the rear. On the way back, with the k10 in tow, anything above 70 would start to bring the temp up. Didn't really want to tow faster than about 65 anyway, just brought it up to see how it would do. To be honest, I didn't even think it would have the power to break 70 with the other truck behind it. That's a lot of air to push, with the k10 lifted and on a trailer.

[manimal]

Check out the dieselplace. I think you've got a great 'Burb. I am going to convert my '89 to a 6.2. Diesel and Gas prices around here are about 5 cents difference,so I dont have a problem going from 8mpg to 16/18mpg and pay 5 cents more than regular unleaded!

[ishta]

Any luck on lifting it? I have an 88 R20 2wd that came lifted from the PO and not too happy with his he did it. I think he put taller springs in and due to that I have no travel and its very bouncy. Upper a arms are resting on the spring cups. Plus I have negative camber. Looking for alternatives.
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